Exstrophy of the bladder occurs once in about 29,000 births. Five males to one female are so afflicted. That the male generative organs are more complex, that deficiencies in the anterior median line occur most frequently in the male, and that deficiencies in the posterior median line occur with more frequency in the female sex probably account for this difference. The mortality during infancy is 60 per cent. An exstrophied bladder may become carcinomatous. A few cases have been reported. CAUSE This congenital defect is best explained on a mechanical basis—an intra-uterine rupture of a completely formed bladder. The first stage in the process is the closing up of the urethra, causing retention of urine. The pubic bones, at this time scarcely cartilaginous, and still ununited, are kept apart until they become hardened. At the same time the rectus muscles are kept apart, so that little by little, by the